Table of Contents
- One of the most common trouble calls for HVAC heating and cooling
- Basic checks of the HVAC System thermostat to see if it is broken or?
- The basics of the thermostat for an HVAC system
- Learn what a heating anticipator is and what type of thermostat uses them.
- Fixing a Broken Thermostat for an HVAC System
- Finally, lots of related useful links to help you learn your heating and cooling HVAC system
Troubleshooting Broken Thermostats - The main connection between the air conditioning and heating system and the end-user is the thermostat. Beyond the air conditioning and heating thermostat, many people know nothing about the HVAC systems that keep them comfortable year-round. While the thermostat may be the problem, make sure you eliminate other possible heating and cooling problems.
There comes a time when the thermostat has a problem or the end-user wants to replace the thermostat because they think it is a broken thermostat. It is not uncommon for a person to call an HVAC contractor and tell the secretary that they think the thermostat is broken because their air conditioner or heating system does not work.
Troubleshooting Broken Thermostats
Fixing a Broken Thermostat | Professional Help
In some instances, this is the case while in others the thermostat is not broken but something is wrong with the air conditioning and heating equipment that needs to be repaired. In either case, it is usually best to call an HVAC professional to look at the problem especially if you want to replace the thermostat. There are a few things you can check with your thermostat before you call an HVAC professional. The thermostat may be the problem but first, make sure to double-check the simple things first. Therefore, a little thermostat troubleshooting is in order.
Common Trouble Signs | Troubleshooting Broken Thermostats
There is a possible quick fix to the broken thermostat.
- Check the power circuit at the circuit breaker and the HVAC equipment.
- If the thermostat is battery-powered try replacing the batteries on the thermostat.
- Make sure to double-check the components and settings in the program for a digital thermostat.
- Check for drafts and other location problems.
What To Check - Detailed Checklist | Troubleshooting Broken Thermostats
- An air conditioning and heating thermostat, even if it is a digital thermostat, is simply a temperature switch that turns the air conditioning and heating system on and off. As with any switch, it needs electricity to function or cause a function with the air conditioning and heating equipment. Most residential and light commercial thermostats are powered by 24 volts A.C. The thermostat gets this 24 volts A.C. from the air conditioning and heating equipment. Usually, this power comes from an air handler in an air conditioning and heating split system and from the main unit for air conditioning and heating package systems.
Power Switches and Circuit Breakers | Troubleshooting Broken Thermostats
- Check the circuit breaker for the air handler or furnace to make sure it is not tripped. Also, check the power switch which should be located near the air handling unit. It is not uncommon for people to mistake these switches for a light switch and turn them off. They unknowingly just turned the power off for their air conditioning and heating equipment including their thermostat. That is when they begin to think they have a broken thermostat. If you have a digital thermostat the power display and the thermostat power display light may not function if you have this problem. Some air conditioning and heating thermostats use batteries to power the backlight which takes us to number two in air conditioning and heating thermostat troubleshooting. Check the power switch and breaker to ensure the power is on before assuming you have a broken thermostat
Fixing a Broken Thermostat | Troubleshooting Broken Thermostats
The back display light for the digital thermostat does not function but the air conditioning and heating system works fine. Check the batteries as some digital thermostats require AA or AAA batteries for the backlight to function on the thermostat.
Types of Digital Thermostats for HVAC Systems | Troubleshooting Broken Thermostats
There are two main types of digital thermostats; Digital thermostats that use batteries for the backlight to function and digital thermostats that use the power from the air conditioning and heating equipment. If you don’t know which kind of air conditioning and heating thermostat you have then opened the thermostat up and look inside. If you don’t see any batteries or a battery compartment inside the thermostat then your thermostat uses power stealing technology.
It is probably an older model digital thermostat. If it is a programmable thermostat then every time you lose power you will lose the program inside. Finally, this takes us to the next step in air conditioning and heating thermostat troubleshooting.
Thermostat Troubleshooting 101 | Troubleshooting Broken Thermostats
- The thermostat may have Power Problems - Check the Power
- Location
- Drafts
- HVAC System Anticipators
- Mechanical Thermostats for HVAC Systems
The Program is Gone | Troubleshooting Broken Thermostats
Fixing a Broken Thermostat - Check the Power
The programmable thermostat is always losing its program. Is it a broken thermostat or simply a malfunctioning thermostat? This is most likely one of the older thermostats that use the power from the HVAC system. Additionally, every time you lose power you lose the program inside the thermostat. The thermostat may have power problems or it could be coming from the HVAC system. Furthermore, programming a programmable thermostat may be a chore for many people to figure out. Therefore, a problem like this can be frustrating especially if you live in an area where there are constant power failures.
The only solution to this problem is to replace the thermostat with one that uses power stealing technology. This should solve the problem. This type uses power from your HVAC system to hold the programs. Additionally, it has a battery backup just in case you lose power to your HVAC system. Lastly, this can save you lots of trouble and frustration and solve the problem. Finally, it keeps you from reprogramming the thermostat over and over again when power failures occur.
If the problem is persistent with the thermostat it is important to get back to thermostat basics.
Fixing Broken Thermostats - The Basics | Troubleshooting Broken Thermostats
Location and Room Temperature
Is the heating and cooling thermostat installed in the proper location? You want the thermostat to read the natural room temperature. This is very important as a thermostat installed on a wall that has high heat gain or heat loss will never offer you comfort as it will react mostly to the temperature of the wall and not the air in the living space. You want the thermostat to sense room temperature and not be influenced by direct sunlight or other heat sources.
Additionally, thermostats installed where direct sunlight can hit the thermostat are going to be a problem also. This will give you false readings and cause your heating and cooling HVAC system to run erratically. Furthermore, a thermostat located near an outside door or window will be affected every time the door or window is opened or closed.
A thermostat should be located close to the return (where the filter is installed) so that it senses and reacts to the air returning to the air handler for conditioning. Additionally, thermostats located near heat sources like hot or cold water pipes, radiant heaters, fireplaces, electrical devices that produce heat, etc… will never offer accurate temperatures and conditioning for the room(s). If the thermostat is affected by other heat sources other than room temperature, it will appear as a broken thermostat or malfunctioning thermostat.
Drafts | Troubleshooting Broken Thermostats
Is there a big hole behind the thermostat that will feed cool or warm drafts to the back of the thermostat? All thermostats have a hole behind them where the wires come into the thermostat from the air handling unit. Check this and if you find a big hole behind the thermostat stuff some insulation in this hole and cover it with a piece of tape. Finally, this will prevent drafts from affecting the thermostat and your HVAC system should maintain proper room temperature.
Remove the thermostat cover and make sure to check the hole in the subbase. This is where the wires come from the wall and are only seen when the cover is removed from the subbase. This can cause your heating and cooling system to cycle unnecessarily because the draft is causing an invalid temperature reading. Make sure to remove the cover and check for this problem. Lastly, make sure the hole is insulated to prevent drafts from affecting the temperature reading on the thermostat. When finished, make sure to replace the cover and test.
Anticipators | Troubleshooting Broken Thermostats
Has the heating anticipator been properly set by a qualified air conditioning and heating technician? It is for the heating system operation. The heat anticipator is on mechanical non-digital thermostats. Additionally, it needs to be set according to the amp draw on the heating system control circuit. The heat anticipator offers a small amount of energy savings and prevents thermostat overshooting for you. Furthermore, it shuts off the main burners because the fan will continue to run and dissipate the heat. When this is not set properly, your heating system will not cycle properly. Therefore, make sure your heating system anticipator is set to the proper setting.
The heat that remains in the furnace or heater. Digital and programmable thermostats have built-in heating and cooling anticipators. They automatically set themselves with no manual adjustments. The mechanical thermostat needs a manual adjustment for the heating system. You need a tool called an amp meter to determine the proper setting. Finally, the cooling anticipator in the mechanical thermostat requires no manual adjustment.
Mechanical Thermostats | Troubleshooting Broken Thermostats
Fixing a Broken Thermostat
The thermostat may not be level. If you have a mechanical thermostat with a mercury bulb switching mechanism inside it this thermostat needs to be level. If the thermostat is not level you never get an accurate temperature in the residence or business. A level thermostat will solve the problem of an inaccurate thermostat.
Additionally, if the thermostat components are dirty you can use a slight amount of compressed air or a small soft brush to gently clean the dirty components inside the thermostat. As a technician, I often carry a can of the computer cleaning compressed air and a small soft brush.
I gently clean the inside components and check the other things noted above. It is important to use a soft brush or compressed air for this as you do not want to damage any of the components. Using a soft brush or compressed air to clean the components will solve the problem of any dirt causing the issue.
Other problems that can occur with your air conditioning and heating thermostat include power surges that can cause a malfunctioning thermostat or broken thermostat. Those other problems need to be discussed with an Heating and Cooling HVAC professional. Furthermore, these problems can be technical, require professional thermost troubleshooting, and require special tools to fix. They can solve the problem with a broken thermostat quickly and efficiently. It is always a wise choice to call in an Heating and Cooling HVAC professional when you have problems with your air conditioning and heating equipment, Lastly, that includes thermostat troubleshooting for your air conditioning and heating thermostat.
Troubleshooting Broken Thermostats
Heating and Cooling - Troubleshooting Broken Thermostats
Heating and Cooling Thermostats Color Codes video for basic thermostat troubleshooting and replacement.
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UVC Light to Kill Viruses and Other Airborne Harmful Things that Affect Health
For additional protection, you can also use UV Light that will kill harmful viruses and bacteria inside the airflow of the air handler. In labs, researchers used a spectrum of ultraviolet light called UVC to kill viruses. This product requires professional installation so it will turn on and off with the blower fan in your air handler but it will offer the protection you need for you and your family from any viruses.
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Hello Richard,
I just had a sensor replaced that had burned out on the furnace. Ever since, the Honeywell Digital non-programmable thermostat (no model number) keeps resetting itself to 75 degrees every few hours. Have tried new batteries, shutting it off and on, etc., but nothing will make it hold a setting for more than a short time. Do you know of any way to make it stop resetting, or do we need a new thermostat? Thank you!
The power for most thermostats comes from the furnace or air handler. That, in most furnaces and air handlers, is where the transformer is that provides power for the low voltage circuits in your HVAC system. I would check to make sure that the thermostat has not been programmed to some obscure setting. After that I would cycle the power off and on to the furnace or air handler and see if the thermostat held its setting. If not then, barring no other checks for your particular system, I would replace the thermostat.
I have a Carrier HVAC unit with digital thermostat. Purchased unit in June 2009. Currently on 5th compressor, replaced coil at 6 mos. Thank God I Purchased 10 yr parts & labor warranty. But now having problem w/thermostat. Set on 65. Furnace just keeps running, have to adjust temp down to get unit to cut off. And while it was cold here couple days temperature fluctuates on thermostat from 64 to 65 causing auxiliary heat to come on. Opening the cover to reset temp can also trigger temp displayed to show lower temp when cover opened. My heat ran nonstop last night & today while at work. Have never replaced thermostat with all other problems. What is “life” of thermostat typically? Does this sound like thermostat problem? Sorry to be long winded. PS I hate this HVAC unit. Thank you for your help
I’ve seen antique thermostats work just fine along with newer thermostats. Many times, people think something is wrong with their thermostat when it is really the equipment. The temperature has been extremely cold recently so, from what you are describing, it is possible there is nothing wrong with the system all. It is simply trying to keep up with the heavy demand placed on it from the cold weather. Most HVAC systems, when installed properly, take into account an average degree day for the area where you reside. When temperatures go to the extreme then your system will work overtime to keep up. Without being there to check it out and only going by the information provide I can only make assumptions here but I have been on trouble calls (in extreme temperatures) where I found nothing wrong with the system. I can only recommend to the people to add more insulation or consider getting their house wrapped and have old doors and windows replaced. Weather-proofing your home can go a long ways in saving the energy your HVAC system produces. The average degree day is one factor mentioned above for properly sizing your system……………some other factors involved in properly sizing the system are materials and insulation in the home. These are used for heat loss and heat gain calculations. I am only surmising your system is working properly. If you are uncomfortable call your HVAC contractor to check it out.
I just replaced an older digital honeywell thermostat that kept shutting off due to low battery. Each time I would replace the battery in that previous unit, it would sometimes work fine for months, other times only for a few hours and then the low battery indicator would start again. Where we live, sub zero temps outside right now mean that a few hours without heat drops the temp inside pretty drastically. We woke up with the temp inside at 59 because the thermostat had shut off sometime during the night. I assumed that it was going bad so I replaced it with a new Honeywell digital thermostat with brand new batteries. It had been working for about 4 hours when all of a sudden the low battery indicator showed up. Could it be bad wiring going from the thermostat to the furnace? Any suggestions?
Not sure whats going on there. Most thermostats are powered by the low voltage transformer that should be located inside the HVAC equipment. I couldn’t tell you exactly what it is but it is probably a very good idea to call in an HVAC tech to properly troubleshoot the problem.
Hello, I recently had my thermostat replaced. Shortly afterwards I had to have my furnace repaired. The thermostat worked fine up until then. Now it seems to be having issues. The thermostat no longer displays heat on when the furnace is running and the furnace seems to run longer now. Any suggestions? Thanks in advance.
Sounds like an anticipator problem but it could be something else. Is it an older mechanical type of thermostat? If so then there is a manual setting for the heating anticipator inside the thermostat. This would cause the furnace to run longer or shorter depending on the anticipator setting. An HVAC technician can set it for you. The setting is based on the amperage draw of the heating control circuit and requires a special meter to read that amperage draw. Newer digital thermostats are set automatically.
My programmable thermostat is not showing the word aux. the pump does turn on and airhandler. But the 2nd stage heatt does not kick in to help.
The second stage or auxiliary heating (commonly referred to as back-up heating for a heat pump) should only kick in when there is an offset in temperatures. For example, if it is extremely cold outside the air source heat pump will not get enough heat from the air outside to keep up with demand (actually the homes or structures heat loss). The thermostat temperature reading will slowly continue to drop. Typically, depending on the thermostat set up, when the temperature falls 3 degrees Fahrenheit below the current set point only then will the auxiliary heating kick on (via a thermostat command). On some thermostats the offset is adjustable so that can be narrowed to say 2 degrees or expanded to to say 4 degrees. There could also be another problem that needs the attention of a technician to check out. Turn the thermostat setting up by three degrees to see if the auxiliary heating comes on. If it does there is not a problem.
We have a heat pump and on the display inside the house we have a reading for the outside temp. That number says that it is 103 degrees outside and in reality it is 24 degrees outside. This isn’t the thermostat for the house, this is just the reading for the outside temp. What can I do about this? Is it something that I need to be worried about?
Sounds like the temperature sensor needs to be replaced. Technically it is called a thermistor. It is important that this device be installed properly. The thermistor or outside air temperature sensor needs to be installed where no other heat source can cause it to read incorrectly. eg……a dryer vent, a flue, or even in the direct sunlight can cause it to read incorrectly. Additionally, the correct type of wire needs to be used in running the the wire from the thermostat to where the thermistor is located. The wire should 16 or 18 gauge shielded wire as other wiring can have cause incorrect readings. All these things need to be considered including the thermistor can go bad over time for various reasons. Additionally, if the programming in the thermostat ties into the controlling the outside unit when the temperature drops then you will have a problem if the system is an air source heat pump and the thermostat is programmed to turn off the outside unit when the temperature drops below the programmed set point and use the inside back up heat source. Call your local HVAC contractor and have them check it out.
I have a thermostat that is set to 72 degrees but on the left it shows its 14 degrees in the house. What do u think the issue is
Not sure? What kind of thermostat? Has the set up inside the thermostat been changed to Fahrenheit for all settings?
Dear Sir I have a Totaline 8 button programable thermostat. The LCD is reading -HP and bounces back and forth to the normal screen displaying tempature and mode. Unit is currently not working.
The HP with Totaline thermostats typically means it is in Heat Pump mode. If the unit is not running then likely there is a problem with the equipment and not the thermostat.
I have a gas ac package unit the ac has never had a problem , but now the heat will run fine 85% of the time and then randomly not come on after the thermostat clicks. If i reset the breaker it will come right back on. Also it seems to work fine on program, mainly does it when i use the hold button.
Sounds like you need to have a technician look at the unit before you press the button to reset it. Only guessing but it likely an ignition problem and that needs the attention of a trained and qualified technician.
I have to keep turning thermostat on and off for it to work. Is it the thermostat? Evert once in a while you hear it click and it comes on.
Just guessing as you did not provide much information but it is likely something wrong with the HVAC system.
I sprayed disinfectant spray onto the a/c screen that displays the degree number temperature. But now the display is mingle with numbers and words. Will the screen of the thermostat return to normal after it drys? I’m too afraid to tell my parent. ? ):
As with many electronics a thermostat is susceptible to getting wet inside. If you are lucky it will dry out and return to normal operation but it is also likely it is damaged and needs to be replaced.
My temperature control does nothing. Can’t turn it off, set temperature, nothing you touch will respond. This is a Honeywellcontrol for my Rheem 3 ton unit.
Power problem or the thermostat is bad are the likely causes.
My thermostat got hit and the digital screen is broke, that happen a few days ago now the air ant working just the fan in the house I guess, the outside fan ant working… Anyone know what I should do.
Replace the thermostat
We just bought a brand new a/c unit because our old one needed to be replaced as it would constantly only put out cool air. The new one was working for a week before it started to put out cool air again. It is set at 73 degrees as the display shows, but the display says it is 81 degrees in here. I cannot figure out if the thermostat is the issue.
call the installing company. It should be under warranty.
My thermostat will not show anything on the display what can be wrong . And the Air Conditioner is not working !
I can only guess but you most likely have a problem with power somewhere. Check the breakers and switches for the inside unit. Follow the instructions here before calling an HVAC contractor to repair the problem.
The temperature display on the thermostat shows only one digit. How do we fix it?
replace the thermostat
Honeywell RTH110B thermostat. The digital display is on…fan set to auto. Last night it did not come on at set temp (72)..display shows it is 79. Checked air handler cb …ok. Do I have a thermostat concern or unit in attic.
Thanks in advance.
Not enough information provided to make an solid assessment. The best thing to do at this point is to call a professional to check it out.
We have a digital thermostat that uses power stealing, no battery backup. The thermostat constantly needs to have the time reprogrammed on it (5+ times daily) and sometimes the display goes blank. Heater kicks on/off according to programming just fine. Have verified the circuit breaker is not tripped and the power switch is on. Has our thermostat gone bad? What else can we verify or should we call an hvac technician to have it replaced?
Yes………….it is time to be replaced and preferably with one that has a battery back-up. I have had this type of thermostat before and it is a pain to reprogram every time there is a glitch in the power system.
I have a strange question. We moved into a new house June 6 and it has geothermal heating and cooling. I don’t know anything about these systems. for 2 1/2 weeks it was on 73 and stayed 73 worked great. we did not touch anything because we did not want to mess it up. From out of nowhere it started getting hotter in the house the temp is 80 at times almost unbearable. We had a guy who works on them come out said the air going in fine and temp out fine. He does not no what the problem might be asked me turn down to 70 and leave it. He said keep eye on light on side when I see any lights above green one let him know. I wonder if the thermostat might not be working correctly. I am so hot last night it was colder outside than in here I opened windows in my room. It was fine before I don’t understand what changed. Please give me advice! Should I call a different person to look at it. By the way lights not changed. I swear think warm air comes out sometimes it is too hot in here.
Thanks
Sherrie
It could be anything and yes I recommend you call someone who specializes in geothermal systems. I am guessing your system has a refrigerant leak and it is freezing up sometimes. When it is not cooling you will experience reduced airflow from the vents. Call someone who specializes in this type of system and they will set you straight. And I am only guessing your system has a leak from the symptoms you describe. To be absolutely sure call a geothermal specialist.
This information is helpful and I did learn some. However, I need further trouble shooting. My thermostat is digital with batteries powering the backlight, it has options for heat, cool and fan. Until recently, I was able to take the cover off and “reset” the thermostat so the A/C would kick back on. Now only the fan works, even after several resets and battery changes. Is it my thermostat or an HVAC issue?
From what you are describing Kayla I would say it sounds like an HVAC issue. Best thing to do at this point is to call in a pro to check it out. Good Luck!!
You replaced the batteries and the back light won’t come on what are you do?
Call a professional or replace the thermostat.
how do you check to see if the thermometer itself is faulty? I have a digital thermometer that now always reads 74 degrees. When it’s hot outside the unit runs constantly an eventually shuts off and blows hot air. When it’s cool the temp remainws 74.
If it always says 74 then something is wrong. Check the temperature by using a temperature sensor you know to be reliable to check the temperature near the thermostat. If its bad replace. And it is possible you could have more than one problem there. Call a professional to have it checked out.
I honestly don’t think it’s your t state. Sounds more like it’s low on charge and when it blows warm air, your compressor is kicking off on thermal overload